Not working after Z key enter to add member into array structure

I set two array (two member) into info structure so it has two member to show two button in viewport. I want to add member (addmember event) to insert info array when pressing ‘Z’ keyboard. It was supposed to get three member. But after Z enter and then I key enter (to show inventory) it dose not show up three member. I,m getting error log. Blueprint Script are give below there.

What is this issues and what is best way to solve it?